"We need to bring our people together so they can unite and heal the wounds," said Machar, who was greeted by ministers and diplomats as he stepped out of his plane after a week-long delay that had threatened a long-negotiated peace deal.
Machar, who was originally due back on April 18, headed immediately to the presidential palace to be sworn in alongside his longtime arch rival, President Salva Kiir.
South Sudan declared independence in July 2011 after decades of conflict with Sudan's authorities in Khartoum, with Machar serving as vice-president from then until July 2014 when he was sacked by Kiir.
His delay in returning to Juba under the terms of a 2015 peace deal had infuriated the international community after months of negotiations spent on getting the rivals to return to the city and share power.
"The return of the designated first vice president should open a new chapter for the country. It should allow the real transition to begin," UN peacekeeping chief Herve Ladsous told the Security Council.
Both sides remain deeply suspicious, and fighting continues with multiple militia forces unleashed who now pay no heed to either Kiir or Machar.
Machar's return had been stalled by arguments that at one point, in a country awash with weapons, came down to a dispute about just over two dozen rocket-propelled grenades and machine guns that the force guarding him were allowed to have.
The economy is in ruins, over five million people need aid and over 180,000 people are crammed into UN peacekeeping camps, too terrified to venture outside the razor wire fences for fear of being killed.
Tensions are high, and the days ahead will be critical.
